Splitting and Joining Basic Schemas

docs/literate/acset_join.jl

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+using ACSets
+using Catlab
+using Catlab.Graphs
+
+@present SchTable(FreeSchema) begin
+    Name::AttrType
+    Column::Ob
+    colname::Attr(Column, Name)
+end
+@acset_type Table(SchTable)
+
+j = Table{Symbol}()
+add_part!(j, :Column, colname=:color)
+add_part!(j, :Column, colname=:flavor)
+
+k = Table{Symbol}()
+add_part!(k, :Column, colname=:mood)
+
+l = Table{Symbol}()
+add_part!(l, :Column, colname=:review)
+add_part!(l, :Column, colname=:stars)
+
+@present SchEdgeLabeledGraph <: SchLabeledGraph begin
+    TableName::AttrType
+    tablename::Attr(V, TableName)
+    EdgeLabel::AttrType
+    edgelabel::Attr(E, EdgeLabel)
+    # edgename
+end
+@acset_type EdgeLabeledGraph(SchEdgeLabeledGraph)
+
+n = EdgeLabeledGraph{Table{Symbol}, Symbol, Pair{Symbol, Symbol}}()
+add_part!(n, :V, label=j, tablename=:Tastes)
+add_part!(n, :V, label=k, tablename=:Feelings)
+add_part!(n, :V, label=l, tablename=:Review)
+add_part!(n, :E, src=1, tgt=2, edgelabel=:Tastes => :Feelings)
+add_part!(n, :E, src=2, tgt=3, edgelabel=:Feelings => :Review)
+
+function split(sch::BasicSchema)
+    splayed = EdgeLabeledGraph{Table{Symbol}, Symbol, Pair{Symbol, Symbol}}()
+    tables = map(objects(sch)) do ob
+        obtable = Table{Symbol}()
+        cols = getindex.(filter(x -> x[2] == ob, attrs(sch)), 2)
+        add_parts!(obtable, :Column, length(cols), colname=cols)
+        ob => obtable
+    end
+    foreach(tables) do (name, table)
+        add_part!(splayed, :V, label=table, tablename=name)
+    end
+    foreach(homs(sch)) do (f, src, tgt)
+        s = incident(splayed, src, :tablename)
+        t = incident(splayed, tgt, :tablename)
+        add_part!(splayed, :E, src=only(s), tgt=only(t), 
+                  edgelabel=src => tgt)
+    end
+    splayed
+end    
+
+# stitch this together
+# 1. break tablename into Obs
+# 2. labels becomes columns (attrs)
+# 3. edges become homs
+
+""" Sends the graph internal to ACSets into an ACSet schema""" 
+function Base.join(g::EdgeLabeledGraph)
+    obs = Symbol[]
+    attrs = Tuple{Symbol, Symbol, Symbol}[]
+    homs = Tuple{Symbol, Symbol, Symbol}[]
+    foreach(parts(g, :V)) do id
+        table = subpart(g, id, :tablename)
+        push!(obs, table)
+        attributes = subpart(subpart(g, id, :label), :colname)
+        # TODO AttrType
+        push!(attrs, [(a, table, :Name) for a in attributes]...)
+    end
+    foreach(parts(g, :E)) do id
+        src = subpart(g, id, :src)
+        tgt = subpart(g, id, :tgt)
+        el = subpart(g, id, :edgelabel) # :flavor => :color
+        push!(homs, (Symbol("$(el.first)$(el.second)"), el.first, el.second))
+    end
+    BasicSchema(obs, homs, Symbol[:Name], attrs)
+end
+
+# join(split(sch))
+
+SchAnew = join(n)
+
+@acset_type New(SchAnew, index=[:TasteFeelings])